1. Field of the Invention
Air conditioning control systems for use with variable capacity compressors including separate input signals: a signal from the temperature of air within the space being conditioned and a signal which is indicative of potential evaporator coil freezing.
2. Description of the Prior Art
Jacobs (U.S. Pat. No. 2,855,761) shows an air conditioning system for an automobile in which the system is controlled by a compartment sensor and switch 47, and an evaporator temperature-calibrated pressure sensor and switch 48.
Gerard (U.S. Pat. No. 3,044,271) and Thompson (U.S. Pat. No. 2,940,278) show air conditioning systems with sensors for both compartment temperature and evaporator coil temperature.
Anderson (U.S. Pat. No. 3,250,084) shows a water cooling system having temperature sensing elements in the input and the output lines. The responses of the element are combined to control the cooling system.
Moy (U.S. Pat. No. 3,636,724) shows an air conditioning system in which a single sensor senses both room temperature and evaporator coil temperature and controls the system in response thereto.
Newton (U.S. Pat. Nos. 2,306,463), Stickel (2,320,055), Noakes et al (3,194,499) and Eschbaugh et al (3,738,573) show air conditioning systems which are controlled by piston valves which are controlled by temperature sensors. Newton and Stickel sense both evaporator temperature and air temperature.
Laporte (U.S. Pat. No. 3,214,930) shows an air conditioning control system in which two bulb-type temperature sensors are disposed at separate locations on the evaporator. The fluid systems of the bulbs are connected together so that the lower of the two bulb pressures controls the switch.
Freeman (U.S. Pat. No. 3,025,881) shows a differential valve of the piston type representative of the art. In this type of valve, the two pressures are additive (or substractive).
Roberts (U.S. Pat. No. 3,959,983) shows a variable displacement compressor of the type which is useful in the air conditioning system described herein. Roberts modulates the capacity of a compressor and maintains a constant suction pressure by using a controlled bleed off of crankcase pressure to the suction line in response to variations in absolute suction pressure.